Engine systems on vehicles, such as hybrid electric vehicles (HEV) and vehicles configured for idle-stop operations, may be configured with a laser ignition system. The laser ignition system includes a laser coupled to each combustion chamber for igniting fuel. In addition to initiating cylinder combustion, the laser ignition system may also be used during engine starting to accurately determine the position of a piston in each cylinder. Laser ignition systems may provide various advantages over spark plugs which tend to degrade over time due to chemical changes at the cathode/anode and accumulation of particulate matter.
Laser ignition systems may also be used for misfire detection. One example approach is shown by Martin et al. in U.S. 20160040644. Therein, after a laser ignition system is used to ignite an air-fuel mixture in a cylinder, a temperature profile of the cylinder is sensed over the combustion event via an infra-red sensor. A misfire event is then determined based on the generated temperature profile relative to an expected profile.
However, the inventors herein have identified a potential issue with such an approach. A misfire may be identified when the cylinder does not produce sufficient torque. There may be various reasons for a cylinder to misfire, and a controller may perform different misfire mitigating actions based on the nature of the misfire. In the approach of Martin, if the laser device of the laser ignition system is degraded, the cylinder will also not produce any torque on a combustion event, generating a misfire. Consequently, the controller may be confounded as to the reason for the misfire. For example, it may be difficult for the controller to determine if the misfire was due to laser ignition system degradation, an air-fuel mixture having a richer than intended (e.g., richer than stoichiometric) air-fuel ratio, leaky intake or exhaust valves, a plugged fuel injector, hot cylinder walls, etc.
In one example, the above issue may be addressed by a method for diagnosing the laser ignition system so as to differentiate laser degradation induced cylinder misfire from other misfire causes. One example method includes spinning an engine unfueled to establish a baseline exhaust temperature and then seal a cylinder at a position of negative valve overlap; operating a laser ignition device in the sealed cylinder; spinning the engine unfueled to unseal the cylinder; and diagnosing the laser ignition device based on a change in measured exhaust temperature relative to the baseline exhaust temperature. In this way, a laser ignition system may be more robustly diagnosed while minimizing noise factors.
As an example, after an engine soak to ambient temperature conditions during a key-off condition, an engine controller (e.g., an engine's powertrain control module or PCM) may wake up to diagnose the laser ignition system. The controller may spin the engine unfueled for a duration (e.g., for 15 seconds) and a baseline temperature for the (unfueled and un-combusted) exhaust stream may be established with the laser ignitors coupled to all the cylinders deactivated. In one example, where the exhaust passage includes a particulate filter, the exhaust stream temperature may be measured by a temperature sensor coupled to the filter. Once the baseline exhaust temperature is established, the controller may spin the engine slowly to a position where a first cylinder, selected for laser ignition diagnostics, is sealed. Specifically, at the position, both the intake and exhaust valves of the selected first cylinder may be fully closed, such as at a position of negative intake to exhaust valve overlap. The laser of the sealed cylinder is then activated, which causes heat to be generated in the cylinder (since there is no fuel to combust), and then trapped therein due to the valves being closed. After a duration of laser operation, the laser is deactivated and the engine is spun, unfueled, to a position where the valves are open and the heated air from the cylinder is released. A subsequent rise in the exhaust temperature (relative to the baseline value) following the engine spinning indicates that the laser coupled to the first cylinder is functioning. Else, if the temperature does not rise, it may be determined that the laser coupled to the first cylinder is not functioning and a diagnostic code with a unique identifier for the first cylinder may be set. The controller may then proceed to re-establish a baseline exhaust temperature and similarly assess remaining cylinders, one at a time, by sealing the cylinder and operating the laser ignition device in the sealed cylinder.
In this way, the ability of laser ignitors to heat a metallic object upon impingement of the laser beam can be advantageously leveraged to diagnose the laser coupled to each cylinder. The technical effect of sealing a cylinder by spinning the engine to a position where cylinder valves are closed, and operating the laser in the sealed cylinder, is that a temperature inside the cylinder can be raised. By then spinning the cylinder to open the valves, the additional heat can be transferred to an exhaust stream. By comparing the change in exhaust temperature following the opening of the cylinder valves relative to a previously established baseline temperature, the heat transfer from the laser ignition device can be measured, and the functionality of the laser can be inferred. By relying on the laser's motive energy and resultant heat generation during engine-off conditions, the laser can be diagnosed robustly and without confounding the results with noise factors from engine combustion. By performing the diagnostic sequentially on all engine cylinders, individual cylinder laser systems can be accurately diagnosed. By enabling a laser ignition system to be diagnosed, engine misfires due to ineffective laser operation in an engine system configured with laser ignition can be better distinguished from other misfire causes. Consequently, engine misfires may be mitigated in a timely and appropriate manner.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.